The present invention relates to a non-brittle silicide target suitable for forming a ZrO2.SiO2 or HfO2.SiO2 film that can be used as a high dielectric gate insulating film.
The thickness of a dielectric gate insulating film affects the performance of an MOS transistor significantly, and should be such that the boundary to the silicon substrate is electrically smooth, and the mobility of carriers does not deteriorate.
Heretofore, an SiO2 film has been used as the gate insulating film, and this has been most excellent in boundary characteristics. An SiO2 film has characteristics such that the thinner the SiO2 film used as the gate insulating film is, the larger the number of carriers, i.e. electrons or holes is, thereby increasing the drain current.
For these reasons, the SiO2 film has been thinned to lower current and voltage values within the extent not to cause dielectric breakdown. However, there is limitation in thinning such SiO2 films, and when the thickness of the SiO2 film is decreased to 2 to 3 nm or less, a tunnel current flows and the SiO2 film cannot function as an insulating film.
On the other hand, although transistors have been downsized, this is meaningless as long as there is limitation in the thickness of the SiO2 film that functions as a gate insulating film as described above, and the performance of transistors has not been improved.
Also, in order to lower the power voltage of an LSI to save power consumption, the gate insulating film must further be thinned. However, since there is a problem of the dielectric breakdown of the gate when the thickness of the SiO2 film is 3 nm or less, decrease in film thickness itself has limitation.
For the above-described reasons, high dielectric gate insulating films are recently studied for substituting the SiO2 film. The high dielectric gate insulating films of interest include a ZrO2.SiO2 film or HfO2.SiO2 film.
These high dielectric gate insulating films are characterized in that the capacity equivalent to the capacity of an SiO2 film can be attained by a relatively thick film, and tunnel leakage current can be inhibited. Also, since these gate-insulating films can be considered to be SiO2 films to which Zr or Hf is added, their interfacial characteristics can be expected to be similar to those of SiO2.
Consequently, there is a need for a sputtering target that can produce a high-quality ZrO2.SiO2 or HfO2.SiO2 high dielectric gate insulating film easily and reliably.
In order to solve the above-described problems, the object of the present invention is to provide a non-brittle silicide target suitable for forming a ZrO2.SiO2 or HfO2.SiO2 film that can be used as a high dielectric gate insulating film that has properties to substitute an SiO2 film, and a method for manufacturing such a silicide target
According to a first embodiment of the present invention, there is provided a non-brittle silicide target for forming a gate oxide film made of MSi0.8-1.2 (M: Zr, Hf).
According to a second embodiment of the present invention, there is provided the non-brittle silicide target for forming a gate oxide film according to the first embodiment, wherein no free Si is present.
According to a third embodiment of the present invention, there is provided the non-brittle silicide target for forming a gate oxide film according to the first or second embodiments, made of the single phase of MSi.
According to a fourth embodiment of the present invention, there is provided the non-brittle silicide target for forming a gate oxide film according to the first or second embodiments, made of a mixed phase of at least two selected from MSi, M5Si4, and MSi2.
According to a fifth embodiment of the present invention, there is provided the non-brittle silicide target for forming a gate oxide film according to any of the first to fourth embodiments, wherein the relative density is 99% or more.
According to a sixth embodiment of the present invention, there is provided the non-brittle silicide target for forming a gate oxide film according to any of the first to fifth embodiments, wherein the average crystal grain diameter is 30 xcexcm or less.
According to a seventh embodiment of the present invention, there is provided the non-brittle silicide target for forming a gate oxide film according to any of the first to fifth embodiments, wherein the average crystal grain diameter is 10 xcexcm or less.
According to an eighth embodiment of the present invention, there is provided the non-brittle silicide target for forming a gate oxide film according to any of the first to seventh embodiments, wherein the transverse rupture strength thereof is 200 MPa or more.
According to a ninth embodiment of the present invention, there is provided a method for manufacturing a non-brittle silicide target for forming a gate oxide film consisting of MSi0.8-1.2 (M: Zr, Hf), comprising the steps of mixing hydrogenated metal (M) powder and Si powder in a mole ratio of 1:0.8 to 1:1.2, and baking and sintering the mixture.
According to a tenth embodiment of the present invention, there is provided the method for manufacturing a non-brittle silicide target for forming a gate oxide film according to ninth embodiment, wherein dehydrogenation and silicide synthesis are carried out by heating during baking.
According to an eleventh embodiment of the present invention, there is provided the method for manufacturing a non-brittle silicide target for forming a gate oxide film according to the tenth embodiment, wherein baking is performed at a temperature between 600xc2x0 C. and 800xc2x0 C.
A ZrO2.SiO2 film or HfO2.SiO2 film that can be used as a high dielectric gate insulating film having properties to substitute an SiO2 film can be formed by oxygen reactive sputtering using a ZrSi or HfSi target.
The present invention provides a silicide target made of MSi0.8-1.2 (M: Zr, Hf), a silicide target made of the single phase of MSi that contains no free Si, or a silicide target made of a mixed phase of at least two selected from MSi, M5Si4, and MSi2.
The M/Si mole ratio required for a high dielectric gate insulating film is 1:1. To go so far, when a high dielectric gate insulating film is produced in a prescribed mole ratio, it can be produced from a mixed phase of a composition extremely deviated from the desired mole ratio, such as metal powder and Si powder or MSi2 powder.
However, it has been known that a free Si phase takes significant part in the occurrence of metal silicide particles. In other words, it has been considered that when a sputtering target of a structure having a mixed phase of silicide and Si is sputtered, the irregularity of the surface caused by difference in sputtering rates between the Si phase and the metal silicide phase becomes prominent, resulting in increase in the number of particles.
According to the present invention, since free Si is eliminated, and the components are limited to three phases of MSi, M5Si4, or MSi2 close to the desired mole ratio, the irregularity of the eroded surface caused by difference in sputtering rates can be minimized, and the occurrence of particles can be prevented.
The above-described silicide target for forming gate oxide films has a disadvantage of high brittleness. According to the present invention, the relative density is 99% or more, and the average crystal grain particle diameter is 30 xcexcm or less, preferably 10 xcexcm or less. Thereby, a non-brittle silicide target for forming gate oxide films with a transverse rupture strength of 200 or more MPa can be obtained.
If the relative density is less than 99%, and the average crystal grain particle diameter exceeds 30 xcexcm, brittleness is lowered due to the shortage of density, resulting in poor machinability. Furthermore, increase in the number of particles is caused due to the breakdown and scattering of brittle crystals. Therefore the above-described ranges are preferable.
In order to manufacture a non-brittle silicide target for forming gate oxide films made of MSi0.8-1.2 (M: Zr, Hf), hydrogenated metal (M) powder and Si powder are mixed in a mole ratio of 1:0.8 to 1:1.2, and the mixture is baked at a temperature between 600xc2x0 C. and 800xc2x0 C.
Although the use of Zr powder and Hf powder can be considered, there is a problem that Zr powder and Hf powder are highly susceptible to oxidation, and fine powder may cause spontaneous combustion.
Therefore, in order to prevent such spontaneous combustion, hydrogenated zirconium or hydrogenated hafnium is used. These hydrogenated powder and silicon powder are finely ground to an average particle diameter of 10 xcexcm or less. The use of these fine powders enables highly densification in sintering.
Heating on the above-described sintering, dehydrogenation and silicide synthesis can be achieved. Dehydrogenation starts from 600xc2x0 C. Sintering is carried out in a vacuum (1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x922 Torr), in a slight hydrogen atmosphere because of dehydrogenation.
As described above, in heating synthesis, by performing dehydrogenation and silicide synthesis simultaneously at a low temperature at which the growth of grains does not occur, the growth of grains can be prevented, the heated powder can be maintained fine, and the average crystal grain diameter can be 30 xcexcm or less even after sintering. If the heated powder aggregates, coarse grains remain and the density lowers because the coarse grains are difficult to grind finely before sintering.
In the present invention, since the material powder is sintered at a low temperature, the growth of crystal grains can be prevented, and high densification can be achieved by sintering.
The densified silicide target of a relative density of 99% or more has a transverse rupture strength of 200 MPa or more.
The densified silicide target of the present invention has the effect to prevent the occurrence of particles caused by pores during sputtering, or the breakdown and scattering of the brittle structure.